1. Field of the Invention
The present invention relates generally to micro-fluid ejection devices and, more particularly, to a fin-shaped heater stack and method for formation.
2. Description of the Related Art
The realization of ultimate inkjet print quality is influenced by several factors, of which one important driving force is the reduction of droplet size and spacing to the minimum detectable limits of the human eye. A desirable goal might be to achieve 1.5 pL drops placed at 1800 dpi. However, given current inks, flow features and nozzle materials, ejector and circuit design, and thin film materials in the heater stack, any printhead that attempts to achieve this goal would be thermally limited due to extreme heat generated on the chip, and specially limited by heater dimension. In order to maintain competitive print speeds, the chip would rapidly rise to >>100° C., eliminating drop-on-demand capability. Conversely, reducing the fire frequency for thermal management would require such a dramatic decrease that the print speed would be extremely slow. On the other hand, in order to maintain adequate drop velocity, certain heater area is required. The solution to this dilemma is to reduce the energy required per heater fire, and remove heater dimension as a limiting factor.
The input energy to an inkjet heater is consumed in several ways. A portion of this energy is transferred to the ink and used beneficially for bubble formation. However, a large portion of the energy is dissipated in the materials over and under the heater. Therefore, by minimizing this waste heat into the heater underlayers and/or overcoats, the total required input energy to the heater can be reduced while still transferring the same amount of energy to the ink. For an intrinsic 1800 dpi heater array, heater pitch is ˜14 μm. However, most heater designs require ˜10 μm heater width, which makes it difficult to form flow features and chamber walls. Also as in previous ultra-low energy heater stack designs, a thin overcoat is a common requirement. However, reliability is a huge concern for such designs, since water hammer and cavitation forces could easily damage such thin layer(s).
Thus, there is a need for an innovation that will improve heater ejector efficiency, increase heater density, reduce inkjet drop size, shrink heater chip size and eliminate heater dimension as a limiting factor.